A variety of existing building blocks can be made by folding a sheet of cardboard. For example, blocks of this type have been disclosed in U.S. Pat. Nos. 3,665,669, 3,702,520, 4,608,799, 5,125,867, 5,281,185 and 5,662,508. In each case, the blocks are stackable and may be releasably interconnected. However, each of these blocks has problems, as discussed below.
In U.S. Pat. No. 3,665,669, each building block has two tabs, aligned in a single line, that protrude from an edge of one side of the block, and also has two slots on an opposite side of the block. Interconnections are formed by inserting the tabs of one block into the slots of one or two other blocks. These interconnections allow a straight wall to be built, but do not allow a corner to be built in which tabs from blocks in one wall are inserted into slots of blocks from another wall. U.S. Pat. No. 3,702,520 is similar, but better able to handle corners. Each block may be folded in such a way as to provide either two tabs in a row down the center line of the block (for making a straight wall) or three tabs, one of which is aligned with the center line of the block and two of which are transverse to the center line (for making a corner). However, the blocks disclosed by both of these patents have problems. First, the connections are not sufficiently rigid. For example, this lack of rigidity makes the blocks impractical for use in many cantilevers or other structures that put substantial torque on an unsupported end of a block. Second, the tabs do not wear well when repeated insertion and release of the tabs occurs. Third, the blocks may be used only for making a straight run of a wall (or, in some cases, a corner). For example, two blocks may not be connected in the shape of a “T” or a cross.
In U.S. Pat. No. 5,662,508, a block has four semicircular tabs, each protruding from the top of the block, with two tabs in a line on one edge of the top and two tabs in a line on an opposite edge of the top. Each block also has a total six semicircular holes on its sides, each at the bottom of a side, with two holes on each long side and one hole on each short side. Each block also has a slot at the center of the bottom side, running transverse to the long axis of the block. An interconnection between two blocks that are aligned in parallel may be formed by inserting semicircular tabs of one block into semicircular holes of another block, and then bending the tabs to releasably lock them in place. An interconnection between two blocks that are transverse to each other may be formed by inserting a semicircular tab of one block into a center slot of another block. These blocks, however, suffer from each of the same problems as U.S. Pat. Nos. 3,665,609 and 3,702,520, discussed above. In addition, the semicircular holes detract from the appearance of the block. For example, a wall made of these blocks would have numerous semicircular holes in it.
In U.S. Pat. No. 4,254,574, each block has a polygonal raised rim on one side and a polygonal hole on an opposite side. Interconnections are made by inserting a raised rim of one block into a hole of another block. These blocks, however, suffer from each of the same problems as U.S. Pat. Nos. 3,665,609 and 3,702,520.
The above patents do not disclose how to fold cardboard in such a manner as to form multiple, parallel rows of protuberances on a single side of a block. Multiple rows of protuberances (similar to a basic Lego® plastic brick) are desirable because they allow for a more rigid interconnection between two blocks.
In U.S. Pat. Nos. 4,608,799, 5,125,867 and 5,281,185, the blocks are made from a semi-rigid material such as cardboard. They have slots or holes into which connectors are inserted. The connectors are separate from the blocks, and made of a different material, such as plastic. The connectors come in a variety of shapes (depending on the patent), such as flat connectors that are circular, semicircular, or rectangular, flat connectors that are polygonal with teeth, or conical connectors with flanges. However, the interconnections (and in particular, the apertures such as slots or holes) do not wear well when subjected to repeated insertion and release.
In all six of the above patents, the manner of interconnection is not similar to that of a Lego® plastic bricks. This is a disadvantage, because end users must be instructed on how to interconnect the blocks.